Finance Minister Grant Robertson is looking for and cash from the investment community.

He has given a speech at an event run by Auckland Chamber of Commerce and Massey University, confirming his intention to address big long-term investment projects.

The Government has put aside $42 billion to fund various schemes over the next four years, including Kiwibuild and rail projects.

However, he told the audience that that won't be enough and that he's looking for new ways to finance infrastructure.

Public-private partnerships will be on the table, and Robertson says he wants to work with the investment community on other ideas.

He says there is a funding gap in Auckland that is up to $6 billion alone. 

He is looking at the possibility of new taxes, such as a property "value capture" tax, alongside ideas such as the Auckland fuel tax. 

He also told the Herald that New Zealand officials are expected to seek an exemption to new US steel and aluminium tariffs.

US President Donald Trump has used his executive powers - evoking national security risk - to apply tariffs of 25 per cent on steel and 10 per cent to aluminium but said there would be a 15-day window for nations to make an appeal for exemptions.

The move has fueled fears that it could provoke retaliation by China and the EU sparking a trade war.

Robertson stopped short of condemning Trump's move directly but expressed disappointment at the shift in US policy.

"Clearly it's not the way we want to see world trade go forward," he said. "There's been a lot of effort over a long period of time to reduce tariffs. So clearly it's not a development we favour."

Trump mentioned both Canada and Mexico - US partners in the Nafta trade pact - and Australia, as a valuable ally that would be considered for exemptions.

He made no mention of New Zealand, which exports about $60 million of steel and aluminium to the US each year.

"I'm sure our government officials will be looking towards an exemption and we need to chase that down.

"But we also need to understand a bit more about the extent of the tariffs," he said.

"Does it cover materials that aren't made in the US [by US companies] ... I know a proportion of NZ steel exports are things that aren't made in the US."

Robertson said US developments highlighted the importance of the CTPP multilateral trade deal that was signed in Chile at the same time as Trump announced his new tariffs.

That would open up a range of new markets for New Zealand exporters, he said.

"Nobody wants a trade war because once you get into retaliatory actions it's a slippery slope. From a New Zealand point of view our focus is on making sure that if there is the possibility of an exemption we can get that, and on building much stronger trade deals and export markets."

- with content from NZ Herald